1. Field of the Invention
The invention relates to a differential lock-up assembly for vehicles with a differential gear set which has a main drive housing, a driving pinion gear being rotatable in the main drive housing, a ring gear engaging the pinion gear, a planet carrier secured to the ring gear and rotatably supported in the main drive housing, a set of pinion gears journalled in the planet carrier and a set of bevel gears engaging the pinion gears and journalled in the planet carrier and engaged to output shafts of the differential gear set, and a lockout clutch assembly with a pack of interleaved discs locking the planet carrier to one of the output shafts on the impact of pressurised fluid with the intermediation of a piston and cylinder assembly.
2. Description of the Related Art
It is quite well known in the prior art (see e. g. GB Patent Specification No. 687,341) to provide a differential gear in a vehicle and a differential lock to be able to lock the driven wheels of the vehicle together and, thus, to put the differential gear out of action. The lock-up assembly includes a hydraulic mechanism with a source of pressurised fluid actuating a clutch with a pack of interleaved discs. The hydraulic mechanism has a rotating cylinder and a piston therein whilst the pressurised fluid is introduced from a standing inlet ring into a bore of rotating disc communicating with the pressure chamber of the cylinder. The clutch is outside the bearing base of the ring gear deteriorating the support capacity of the bearing assembly of the ring gear of the differential gear assembly. Therefore, more sophisticated and expensive bearing assembly is necessary as well as an auxiliary back support for the ring gear. Further, the rotating introduction of the pressurised fluid can be put under pressure only at an extremely low rotational speed and the pressure applied cannot reach the value as required for a secure locking operation. The pack of discs are arranged in a closed space, thus, the heat produced by the friction of the discs cannot be led away from the pack of discs.
U.S. Pat. No. 3,605,965 describes a differential lock-up assembly with the conventional parts of differential gear set and a lockout clutch assembly with hydraulic actuation, wherein the rotating pack of discs are to be compressed by a still-standing piston with the intermediation of a simple bearing washer which is exposed to extremely high wear when the pressure necessary for reliable compression of the discs is applied. Further, the discs are mounted through the inner diameter of the bearing assembly of the planet carrier which delimits the measurements of the discs and, as a result, the loadability of these discs. There is an antagonism between the smallest possible diameter of the bearing and the biggest possible outer diameter of the discs. The reaction force of the piston of the hydraulic actuator is led through the discs to the bearing assembly at the other output shaft enlarging the load on it during the whole locking operation. The load is than transmitted onto the main drive housing resulting a deformation of the seat of the bearing. On the other side of the piston, the reaction force of the cylinder is also transmitted onto the main drive housing further deforming it. This deteriorates the running accuracy of the revolving parts. The pack of discs is in a closed space, too, and the dissipation of heat produced between the discs is not possible at all.
In summary, the previously known solutions providing differential gear lock-up operation are quite complicated and they are not suitable for applications under heavy duty conditions with the necessary reliability and duration but, as mentioned above, the need to overcome these disadvantages is quite urgent.